Slice the ciabatta loaf in half horizontally. Gently pull out some of the soft interior bread from both halves to create more room for fillings.

In a small bowl, mix the mayonnaise and sun-dried tomato pesto. Spread this on the inside of the bottom half of the bread. In another bowl, mix olive oil and Italian seasoning, and brush it on the inside of the top half.

Layer the provolone cheese on the bottom half over the spread. Then, layer the meats in this order: mortadella, Genoa salami, hot capicola, and finally the sweet ham.

Top the meats with the shredded lettuce, followed by the tomato slices (seasoned with a pinch of salt and pepper), red onion, and pepperoncini.

Place the top half of the bread onto the fillings. Spread a thin layer of softened butter on the outside of the top piece of bread.

Preheat a panini press or griddle pan over medium heat. Place the sandwich in the press, buttered-top-side-down. Butter the now-exposed top side. Close the press and cook for 4-6 minutes until the bread is golden brown and crisp and the cheese is melted.

Remove from press, let rest for 1 minute, then slice diagonally with a serrated knife and serve immediately.